How to Make Gold Plating Solution.

Gold Electroplating is a method of depositing a thin layer of gold onto the surface of another metal.

Gold plating finds its uses in jewelry, semiconductor industry. It often employed in electronics to provide a corrosion resistant surface.

In this instructable, I am making alkaline gold plating solution which can deposit gold by electrolysis.

Traditionally, such a solutions prepared using extremely poisonous cyanide compounds which are reasonably restricted.

My goal is to make the solution with the publically available chemicals, which are not as toxic to handle. In any case, the final product will be just as poisonous as the traditionally prepared solution.

For this reason, I must warn you. This experiment is extremely dangerous, and I don't recommend anyone without experience to repeat it.

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Step 1: Nitric Acid.

If you already have nitric acid at the concentration 50% or above, you may skip this step.

In order do dissolve gold, we will need to prepare aqua regia. It is a mixture of nitric and hydrochloric acid at molar ratio 1/3. Hydrochloric acid sold commercially under the name of muriatic acid. However, nitric acid is restricted for public use. Therefore it has to be prepared from available chemicals.

There are quite a few ways to make nitric acid at laboratory conditions. On my youtube channel, I am covering two methods.

First, by reacting sodium nitrate with the sulphuric acid followed by distillation. This process produces acid at the concentration of above 90%. At this concentrations, nitric acid is highly corrosive and fuming a toxic nitrogen dioxide gas.

And the second method, which less dangerous, is a concentrating very dilute nitric acid that is commercially available for the public. I am using fractional distillation to concentrate nitric acid from 30% to 50% concentration. However, I could achieve the azeotropic concentration of 68% if I used proper fractionating column.

For the gold plating solution, this method of nitric acid preparation is favorable as it is relatively safer.

For more details, please watch the video.

Step 2: Making Gold(III)Chloride

To make gold chloride, we need to dissolve gold in aqua regia. (mixture of nitric acid and hydrochloric acid at molar ratio 1/3)

In my case, I have 18K gold scrap, but the purity of gold makes no difference as gold will be purified to 24K during the process.

The reaction of gold and aqua regia produces toxic fumes so the process must be conducted outside or in the fume hood.

It takes around 20 minutes for gold to dissolve at room temperature. At the end of the reaction, we have the solution of dissolved gold and copper compounds and solid crystals of silver salts.

Now this solution needs to be filtered, to separate solids from the liquid.

Next, the gold is precipitated out of the solution in its elemental form by the addition of sodium metabisulfite solution.

During the addition, the toxic sulfur dioxide gas produced, so this process can only be conducted in the fume hood or outside.

Once there is no more visible reaction happens during the addition of the sodium metabisulfite, that would mean all of the gold has precipitated.

And the last step is to separate the solid gold and dissolve it in aqua regia once again. This time there will be no solids and the solution will be the red color. Now the acid needs to be evaporated at 120 degrees centigrade to obtain red crystals of gold(III)chloride.

For more details, please watch the video.

Step 3: Final Step, Making Gold Plating Solution.

In the final step, we need to make a strongly alkaline solution of gold chloride and potassium ferrocyanide.

Using this solution and electrical current, we can deposit gold over the surface of other metals.

This solution contains gold cyanide ions, which are extremly poisonous.

Under no circumstances, this solution can be mixed with acids, as it will release hydrogen cyanide gas. (I can't even find the correct word to describe the toxicity of this gas)

Neither it can be disposed of down the drain.

For the details and demonstrations, please watch the video.

If you like my videos, why not subscribe to my youtube channel? I am uploading videos on the regular basis.

Hmm Have you thought of a good hot plate that can reach 500 degrees C or greater and using an Oil bath. Unless the nitric acid reacts with the hot oil this may help control the heat output. Also you should mention what would happen if Nitric acid heat up too high (formation of toxic nitric oxide and nitric dioxide gas). Nice Job though.

Thank you for your guide! Its come in quite handy. I have a question tho, is there any way to plate silver onto copper? Also, does this only work for playing gold onto silver? Is there a diffrent solution needed to plate gold onto copper?

Hi, thanks for your question. It is much easier to plate with silver, and the process does not require the use of poisonous cyanide compounds. However, I've never silver plated before thus my knowledge is only hypothetical. You need a solution of silver nitrate as the electrolyte, and the negative terminal of electrolysis must be pure silver.

If you don't know how to make silver nitrate you can check out youtube channels (NurdRage, or NileRed) they both have great videos on making silver nitrate.

I am not exactly sure about the concentration of silver nitrate solution. Personally, I would dissolve 1g of silver nitrate per 100ml of water. The deposition of silver may take a while, as the conductivity of this solution will be very low. So if thinking logically, the more concentrate the solution of silver nitrate the faster it will be depositing the silver.

The gold plating solution that I made, can also be used to deposit gold on some other metals including copper, stainless steel, brass etc. However, it does not seem to work on zinc metal, and I couldn't figure out why.